Problem: Tiffany is 4 times as old as Umaima and is also 30 years older than Umaima. How old is Tiffany?
Answer: We can use the given information to write down two equations that describe the ages of Tiffany and Umaima. Let Tiffany's current age be $t$ and Umaima's current age be $u$ $t = 4u$ $t = u + 30$ Now we have two independent equations, and we can solve for our two unknowns. One way to solve for $t$ is to solve the second equation for $u$ and substitute that value into the first equation. Solving our second equation for $u$ , we get: $u = t - 30$ . Substituting this into our first equation, we get the equation: $t = 4$ $(t - 30)$ which combines the information about $t$ from both of our original equations. Simplifying the right side of this equation, we get: $t = 4t - 120$ Solving for $t$ , we get: $3 t = 120$ $t = 40$.